The field of the invention is that of integrated optical emission devices comprising a laser emission section and a section for modulating the optical power emitted by the laser, also known as ILM devices, the acronym standing for Integrated laser Modulator. The invention is aimed at an ILM device comprising a laser section and a modulation section produced in a common structure of p.I.n type, the said structure successively comprising a substrate produced from n-doped semi-conductor material, a buried active zone, a p-doped vertical confinement layer and a semi-insulating lateral confinement layer, the part of the structure belonging to the laser section comprising a blocking layer produced from n-doped semi-conductor material disposed between the semi-insulating lateral confinement layer and the vertical confinement layer so as to reduce the leakage current existing between the said layers. The performance and the reliability of the final device is thus improved.

Patent
   7430229
Priority
Jul 08 2005
Filed
Jul 10 2006
Issued
Sep 30 2008
Expiry
Sep 22 2026
Extension
74 days
Assg.orig
Entity
Large
0
3
all paid
1. Opto-electronic device, of the type with laser and integrated modulator comprising: a laser section and a modulation section produced in a common structure of p.I.n type, the said structure successively comprising a substrate produced from n-doped semi-conductor material, a buried active zone, a p-doped vertical confinement layer, the lateral faces of the active zone being surrounded by a semi-insulating lateral confinement layer produced from doped semi-conductor material, wherein the part of the structure belonging to the laser section comprises a blocking layer limited to the laser section produced from n-doped semi-conductor material disposed between the semi-insulating lateral confinement layer and the vertical confinement layer, the modulation section not comprising any blocking layer.
2. Opto-electronic device according to claim 1, wherein the substrate, the vertical confinement layer, the lateral confinement layer and the blocking layer are essentially produced from a first semi-conductor material whose components belong to groups III and V of the periodic table.
3. Opto-electronic device according to claim 1, wherein the blocking layer is produced from Indium Phosphide (InP) or from InGaAsP (Indium-Gallium-Arsenic-Phosphorus) or from InAlAs (Indium-Aluminium-Arsenic) or from a combination of the family of AIInGaAsP materials.
4. Opto-electronic device according to claim 1, wherein the active zone is produced from InGaAsP (Indium-Gallium-Arsenic-Phosphorus) or from a combination of the family of AIInGaAsP materials.
5. Opto-electronic device according to claim 1, wherein the width of the active zone equals about 1 .5 microns and the thickness of the common structure equals a few microns.
6. Opto-electronic device according to claim 1, wherein the thickness of the blocking layer is less than a micron.
7. Opto-electronic device according to claim 1, wherein the structure comprises a screen layer disposed between the substrate and the active layer, the said layer also being produced from Indium Phosphorus (InP).

1. Field of the Invention

The field of the invention is that of optical emission devices comprising an integrated component comprising at least one laser emission section and a section for modulating the optical power emitted by the laser. These systems are also called ILMs, the acronym standing for Integrated Laser Modulator or EMLs, the acronym standing for Electro-absorption Modulated Laser. The modulation section is generally also called an EAM, the acronym standing for Electro Absorption Modulator.

These devices are used mainly in the field of high-throughput digital telecommunications. The throughputs are typically from a few gigabits to several tens of gigabits per second.

2. Description of the Prior Art

It is possible to modulate a laser beam in three different ways. A first method consists in directly modulating the source laser by controlling its feed current. However, this technique does not make it possible to attain the performance necessary for high throughput. It is also possible to use an external modulator, physically separate from the source laser and whose performance is not limited by that of the laser. However, this method poses significant integration and positioning problems. Finally, it is possible to produce an integrated component comprising, on the same substrate, a laser emission section and a section for modulating the optical power emitted by the laser. The best compromise between the desired performance and the technological production and integration problems is thus obtained.

The latter type of device, the ILM, is known and is described, for example, in French patent FR2 675 634. By way of example, an ILM device is represented diagrammatically in FIG. 1. It essentially comprises a laser section 1 and a modulation section 2. As indicated in FIG. 1, the laser is driven by a current I and the modulation section 2 is an electro-absorbant section, on/off controlled by a voltage signal V. At the output of the ILM device, a high-frequency modulated optical signal is emitted (straight barred arrow of FIG. 1).

Generally, the optical emission structure is a semi-conductor laser with a buried stripe also called a BRS structure, the acronym standing for Buried Ridge Stripe. A diagram of such a structure is represented in FIG. 2. It comprises essentially:

This configuration makes it possible to ensure, at one and the same time:

The benefit of this geometrical configuration is to obtain lasers with very low threshold current and with very high switching speed.

Since the appearance of this type of structure in the 1980s, technological developments have made it possible to improve the performance of this type of laser. Structures comprising semi-insulating layers are generally used. Descriptions of this type of structure will be found in French patent FR 91 04636. A diagram of such a structure is represented in FIG. 3. It comprises essentially:

This type of laser is also called SI BH, the acronym standing for Semi-Insulating Burried Heterostructure.

Of course, in ILM devices, the laser section and the modulator section have the same buried structure. Devices having very good performance in terms of thermal dissipation, optical losses, stability of the optical modes and reliability are thus obtained. Moreover, the integration of the two emission and modulation functions in a single component makes it possible to substantially reduce costs.

However, a laser of SI BH type exhibits significant lateral leakage current due to fast decay of the resistivity of the lateral confinement layer when a positive voltage is applied to the structure. This effect is widely known and described. It results from the interdiffusion of the p dopants of the vertical confinement layer and of the dopants of the semi-insulating lateral confinement layer during the step of producing the vertical confinement layer. This leakage current appreciably degrades the performance of the laser.

There exist various techniques for attempting to reduce this problem. We shall cite:

The object of the invention is to propose an integrated component of ILM type comprising at least one laser emission section and a modulation section comprising a technologically well controlled structure of SI BH type exhibiting neither significant leakage current nor significant stray capacitance. Thus, a device according to the invention makes it possible to attain significant performance, compatible with high-throughput digital telecommunications while not exhibiting any particular production difficulties.

More precisely, the invention is aimed at an opto-electronic device, of the type with laser and integrated modulator comprising a laser section and a modulation section produced in a common structure of P.I.N type, the said structure successively comprising a substrate produced from n-doped semi-conductor material, a buried active zone, a p-doped vertical confinement layer, the lateral faces of the active zone being surrounded by a semi-insulating lateral confinement layer produced from doped semi-conductor material, characterized in that the part of the structure belonging to the laser section comprises a blocking layer produced from n-doped semi-conductor material disposed between the semi-insulating lateral confinement layer and the vertical confinement layer.

Advantageously, the substrate, the vertical confinement layer, the lateral confinement layer and the blocking layer are essentially produced from a first semi-conductor material whose components belong to groups III and V of the periodic table.

More precisely, the blocking layer can be produced from InP (Indium Phosphide), from InGaAsP (Indium-Gallium-Arsenic-Phosphorus) or from InAlAs (Indium-Aluminium-Arsenic), the active zone being produced from InGaAsP (Indium-Gallium-Arsenic-Phosphorus).

Advantageously, the dopings of the substrate and of the vertical confinement layer are of the order of 1018 atoms/centimetre3, the doping of the lateral confinement layer is 1017 atoms/centimetre3 and the doping of the blocking layer is of the order of 1018 atoms/centimetre.

Advantageously, the width of the active zone equals about 1.5 microns and the thickness of the common structure equals a few microns, the thickness of the blocking layer is, for its part, less than a micron.

Advantageously, the structure comprises a screen layer or buffer layer disposed between the substrate and the active layer, the said layer also being produced from Indium Phosphide (InP).

The invention relates also to a method of producing an opto-electronic device of the type with laser and integrated modulator comprising at least one of the preceding characteristics. The said method comprises at least the following steps:

characterized in that the method of production comprises, furthermore, the following two additional steps carried out successively between the second step and the fifth step which are:

Advantageously, step 4 of the method is carried out by chemical or mechanical etching.

The invention will be better understood and other advantages will appear on reading the non-limiting description which follows and by virtue of the appended figures, of which:

FIG. 1 represents the basic diagram of an opto-electronic device of ILM type;

FIG. 2 represents a sectional view of a laser with buried stripe of BRS type;

FIG. 3 represents a sectional view of a laser with buried stripe of BRS type with semi-insulating layer;

FIG. 4 represents a first sectional view of an ILM device according to the invention;

FIG. 5 represents a second sectional view in the laser section of an ILM device according to the invention;

FIG. 6 represents a third sectional view in the modulator section of an ILM device according to the invention.

The sectional view of FIG. 4 represents an ILM type device according to the invention comprising a laser section and a modulation section. It essentially comprises a common structure of P.I.N type, the said structure comprising successively:

The laser section comprises a blocking layer 17 produced from n-doped semi-conductor material disposed between the semi-insulating lateral confinement layer and the vertical confinement layer.

The substrate, the vertical confinement layer, the lateral confinement layer and the blocking layer are essentially produced from a first semi-conductor material whose components belong to groups III and V of the periodic table. By way of example, the said first material is Indium Phosphide (InP). The dopings of the substrate and of the vertical confinement layer are of the order of 1018 atoms/centimetre3 and the doping of the lateral confinement layer is 1017 atoms/centimetre3.

The structure is organized as two sections 1 and 2 driven by two independent sets of electrodes 130, 140 and 131, 141 disposed respectively on the lower face of the substrate 10 and the upper face of the vertical confinement layer 16. The electrodes 130 and 131 can be linked together by a common earth. By way of example, these electrodes comprise a first conducting layer which can be of p-doped InGaAs. The thickness of this layer is less than a micron and its doping is of the order of 1019 atoms/centimetre3. On this first layer is deposited the metallic electrical contact proper.

The section 1 corresponds to the laser section and the section 2 corresponds to the modulation section. The laser section 1 comprises a blocking layer 17 produced from n-doped semi-conductor material disposed between the semi-insulating lateral confinement layer and the vertical confinement layer 16.

FIGS. 5 and 6 represent two sectional views of the device of FIG. 4 in two planes perpendicular to that of FIG. 4. These views make it possible to better specify the internal arrangement of the various layers of the structure. In these sectional views, the bottom part of the structure comprising the electrodes 130 and 131 is not represented.

In FIGS. 5 and 6, the active zone 111 is buried within the structure. Its lower face is in contact with the substrate 10. Its lateral faces are in contact with the semi-insulating lateral confinement layer 15, its upper face is in contact with the vertical confinement layer 16. The total thickness of the common structure equals a few microns.

The width of the active zone equals about 1.5 microns and its thickness is less than a micron.

The active zone necessarily comprises a layer 111 of active material which can be, for example, InGaAsP (Indium-Gallium-Arsenic-Phosphorus) or be a combination of the family of AlInGaAsP materials. (Aluminium-Indium-Gallium-Arsenic-Phosphorus). The composition of the active material determines the emission wavelength of the laser, generally situated in the near infra-red for applications in telecommunications. It can however comprise other layers such as a buffer layer 110 or a protection layer 112, the buffer layer 110, because of its mode of growth possesses superior crystalline quality, it is also produced from Indium Phosphorus (InP).

As indicated in FIG. 5, the blocking layer of the laser section is disposed on either side of the upper face of the active zone, between the semi-insulating lateral confinement layer 15 and the vertical confinement layer 16.

The blocking layer is produced from n-doped semi-conductor material which can be, for example, Indium Phosphide (InP) or InGaAsP (Indium-Gallium-Arsenic-Phosphorus) or InAlAs (Indium-Aluminium-Arsenic) or a combination of the family of the AlInGaAsP (Aluminium-Indium-Gallium-Arsenic-Phosphorus) materials. The doping of the blocking layer is of the order of 1018 atoms/centimetre3.

Its thickness is typically a few tenths of a micron.

The blocking layer limits the interdiffusion of the dopants between the vertical and lateral confinement layers 15 and 16. It makes it possible to preserve the semi-insulating nature of the lateral confinement layer without introducing stray capacitances or additional resistances.

As indicated in FIG. 6, the blocking layer is limited to the laser section, the modulation section not comprising any blocking layer. Ionic insulation provides the boundary between the laser section and the modulation section. This therefore eliminates any stray capacitance in the modulation section.

The production of a device according to the invention does not present any particular difficulty.

It essentially comprises the following steps:

The production of the layers by epitaxial growth and their delimitation by chemical or mechanical etching forms part of the knowledge of the person skilled in the art. Examples of methods of this type will be found in French patents FR 2 675 634 and FR 2 820 891.

Kazmierski, Christophe, Le Pallec, Michel

Patent Priority Assignee Title
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